No Vacancy is an evil music band in the movie School of Rock. While not wholly evil, No Vacancy enjoy Dewey's suffering and confusion when he is kicked out, and Theo in particular wants to humiliate Dewey.
Dewey used to be a member of the band, in fact he formed the band in the first place, and is outraged when he is dumped, but Theo explains its his ambition to get loads of money that made him sack Dewey because Dewey was an "embarrassment" to them. Saying it was due to all the "twenty-minute solos, the stage dives," Theo says the band will be more organized and business-like from then on. He also says "we're trying to write a record."
Dewey promises he will own No Vacancy in the gig and they will just be a bad memory for him. This never actually comes to pass, but he says "I feel sorry for you guys." Theo and Neil and Doug introduce Spider to the band as Dewey's replacement, and this also outrages Dewey. They are also implied to not trust each other, due to Theo not telling Spider why he is replacing Dewey, and Neil wanting to keep Dewey in, but Theo outruling him.
Theo is the leader and holds it together through ambition and bullying. He was seen to be Dewey's best friend but it changed when he sacked Dewey. No Vacancy write a new song, which Dewey hears, and they perform it at the Battle of the Bands.
School of Rock seem enamoured by the No Vacancy but Dewey tells them they're hacks. He says they should play the new song Zack invented rather than the one they practiced despite the fact they might not win, but Dewey says its not about winning. In the intervals, No Vacancy are actually impressed that eleven year olds can play instruments as well as they can and congratulate them, all apart form Theo. Despite this, he gets pissed off when No Vacancy win the Battle of the Bands.
No Vacancy successfully get the twenty thousand dollars but it was half-measured win: everyone calls out for School of Rock instead and No Vacancy get shoved offstage to dwell on beer.